Question: Solve for $x$ and $y$ using substitution. ${x+y = 11}$ ${y = 3x+3}$
Since $y$ has already been solved for, substitute $3x+3$ for $y$ in the first equation. ${x + }{(3x+3)}{= 11}$ Simplify and solve for $x$ $x+3x + 3 = 11$ $4x+3 = 11$ $4x+3{-3} = 11{-3}$ $4x = 8$ $\dfrac{4x}{{4}} = \dfrac{8}{{4}}$ ${x = 2}$ Now that you know ${x = 2}$ , plug it back into $\thinspace {y = 3x+3}\thinspace$ to find $y$ ${y = 3}{(2)}{ + 3}$ $y = 6 + 3$ $y = 9$ You can also plug ${x = 2}$ into $\thinspace {x+y = 11}\thinspace$ and get the same answer for $y$ : ${(2)}{ + y = 11}$ ${y = 9}$